Air Defence System / HQ-2A/B / CSA-1 /
SA-2 Guideline

Зенитный
Ракетный Комплекс
С-75 Двина/Десна/Волхов

The S-75 / SA-2 Guideline was the first SAM to
be
used in anger, en masse, and changed the character of air warfare
forever. Depicted Soviet
supplied S-75 / SA-2 Guideline and SM-90 launcher operated by Egypt in
1985
(US DoD)

Introduction

The S-75 / SA-2 Guideline
family of SAM systems remains the most widely exported area defence
missile system, and was supplied in large numbers by the Soviets to
Warsaw Pact nations, Third World Soviet allies and other non-aligned
nations. Over thirty nations deployed one or another variant of the
SA-2, and China manufactured indigenous derivatives well after this
design was out of production in the Soviet Union.

The basic design qualifies as semi-mobile, requiring several hours to
set up or redeploy a battery. Typical battery composition is a single
SNR-75 Fan Song series engagement radar, six SM-90 single rail
launchers, and multiple PR-11AM transporter/transloader trucks carrying
reload rounds for the SM-90s.

Many S-75 operators deploy the system in fixed sites, with revetments
using concreted pads and bays, and/or earthwork berms, to protect the
missile system components.

The PLA reverse engineered the Soviet V-75/S-75 Dvina / SA-2 Guideline
SAM system during the 1960s, including the SNR-75 Fan Song radar, the
SM-90 launcher and the PR-11AM transporter/transloader. Since then the
PLA developed a significantly improved HQ-2B variant.

The Fan Song is the engagement
radar for the S-75/SA-2 family of SAMs. First deployed in strength
during the Vietnam conflict, and later used extensively in the Middle
East and Africa, the SA-2 was the first Soviet SAM to be used in anger
and accounted for large numbers of Western aircraft until electronic
countermeasures were developed. The system was cloned by PLA and still
remains widely in use, even though Russia has replaced it with the
SA-10/20 system.

The are at least six known variants, one of which is a PLA clone.
Details of PLA modifications to the design are not public knowledge.
There are sufficient differences in the PLA designs to regard these as
unique derivatives. The antenna configuration of the PLA variants
generally follow the Fan Song A arrangement.

The SNR-75 family of radars employ, by modern standards, a complex
antenna arrangement which is employed to effect range and angle
tracking of the intended target, and of the transponder beacon in the
tail of the missile round. The proximity fused missile round is
“dumb” in the sense that it is a pure command link design, which
is flown to a collision with the target using a command uplink embedded
in the SNR-75 radar.

1D/13D/DM/DA/DAM/20D/DP/DSU/5Ya23/15D
Surface to
Air Missiles

The configuration of the 1D
through 5Ya23 missiles is a direct evolution of the earlier SA-25/S-25
/ SA-1 Guild, itself evolved from the 1944 German Wasserfall design.
Unlike its predecessors, the S-75 / SA-2 family of missiles were two
stage designs, using a solid rocket first stage booster for launch and
a variable thrust liquid propellant motor sustainer. Midbody cruciform
wings were employed to improve range and turning ability, with canard
and tail winglets for pitch, roll and yaw control and stability.

By modern standards, the missile
design is unusually simple, with most of the complexity in the liquid
propellant sustainer and fuel system. The choice of this sustainer for
two reasons, the first being immaturity of high impulse solid
propellants, the second being in the ability to modulate thrust through
the flight profile.

An important consideration is the
Soviet philosophy of making the missile round as simple and cheap as
possible, and putting the cost and complexity into the engagement
radar. The operational economics of this model were to minimise the
cost of the expendable component of the weapon system.

The nose of the missile houses
the radio proximity fuse. In early variants this was the 5E11 Shmel
series, the later Ovod variant, and then the 5E29. Early variants used
separate linear transmit and receive antennas flush with the skin of
the missile, later variants used a characteristic dielectric band
radome. Later variants included programmable ECCM modes, such as
alternating emissions between the two hemispheres of antenna coverage.

Immediately aft of the fuse is
the V-88 series blast fragmentation warhead, which weighs between 190
kg and 250 kg, depending on missile variant. The large warhead size was
intended to produce a large lethal envelope, to offset the accuracy
limitations of the command link guidance and proximity fusing. Warhead
performance evolved over the life of the missile, the early 11D round
producing 8,000 fragments, the 20D 32,000 fragments and the very late
5Ya23 29,000 fragments. Initial fragment velocity was 2,500 m/s. The
timing of the proximity fuse trigger point was programmable via the
command uplink, with shorter delays for closing versus receding
targets. Lethal radius was nominally 60 metres (~400 ft lethal
diameter).

Much of the missile's internal
volume is occupied with propellant tanks for the sustainer engine.

The 43 kg dry weight Isayev
S2.711
(S5.711) liquid
propellant powerplant burns a hypergolic propellant mix. The oxidiser
is either AK-20F or AK-20K fuming nitric acid melange depending on the
motor variant, comprising ~80% nitric
acid and ~20% N2O4 with an inhibitor additive.
The fuel is TG-02, comprising 50% isomeric xylidine, 48.5%
triethylamine and 1.5% diethylamine, this propellant mix was
essentially an evolution of the 1944 Wasserfall fuel. The S2.711 used
in early variants produced a thrust rating between 2,650 and 3,000 kp
(5,800 lbf and 6,600 lbf), the later S2.720 used in the 20D round
produced between 2,075 kp and 3,500 kp (4,580 lbf and 7,700 lbf) thrust
using a different propellant mix. Specific impulse for the S2.711 was
224 up to 252.7 kp.sec/kg.

The turbopump for the engine
was fuelled by a tank of OT-155 Isonite
(isopropyl nitrate). The propellant payload permitted a burn duration
between 25 and 60 seconds, subject to thrust profile. All propellant
tanks were pressurised from a compressed air tank.

This fuel system arrangement as used in the earlier 1D through 11D
variants was supplanted in the 20D and later missile rounds. The later
variants used the AK-27I oxidiser, comprising ~73% nitric
acid, ~27% N2O4 and an inhibitor additive.
The fuel was TM185 comprising 56% Kerosene and 40% Trikresol. As this
fuel did not ignite spontaneously, an additional tank of TG-02 “starter
fuel” was employed to ignite the rocket. The later propellant mix was
more energetic and provided better storage life, with the TM185 fuel
being less toxic, and the primary propellant components safer to fuel
and defuel.

The first stage which was used to accelerate the missile at launch used
a PRD-18 solid rocket
powerplant with 2-4 sec burn duration. This design used 14 tubes of
NMF-2 propellant and a variable cross section throat.

The missile guidance system is relatively simple, comprising an
autopilot and a command link receiver, with a missile beacon in the
tail to facilitate tracking by the Fan Song radar.

The command link channel produced four distinct pulse modulated
waveforms. The K1 and K2 waveforms carried climb/dive and left/right
turn commands, the K3 waveform arms the radio proximity fuse, and the
K4 waveform is used to program the proximity fuse delay depending on
missile engagement geometry.

In operation, the Fan Song radar would track the target and
continuously compute an optimal missile trajectory for intercept, while
tracking the missile via its transponder beacon. The uplink would then
be used to continuously drive the missile flightpath as close as
possible to the intended trajectory, in a closed loop scheme.

Two control laws were employed, the
“Treokh Tochek (TT - three
point)” and “Polavinoye Spravleniye
(PS - half correction)” techniques.

The TT control law is essentially a Soviet implementation of Command to
Line of Sight (CLOS), where the missile flightpath is continously
adjusted so that it follows the line of sight between the radar and the
target. While this technique does attempt to minimise flightpath
length, it does not maximise missile range per propellant payload, and
tends to subject the missile, in some geometries, to large transverse
accelerations. The latter facilitated defeat of the missile by high G
manoeuvres.

The PS control law was more sophisticated and used against manoeuvring
targets. An earth bias was often included in the control law when
firing against low altitude targets, to preclude unwanted proximity
fuse initiation, or inadvertent ground collision caused by autopilot
inputs.

The command link guidance scheme and need to carefully select control
laws and radar modes resulted in a need for high levels of operator
skill and a good understanding of engagement geometries. The combat
effectiveness of the S-75 / SA-2 Guideline varied widely as a result,
with Warsaw Pact instructors and their Vietnamese students typically
performing much better in combat compared to their counterparts in the
Middle East.

Production and Exports

The S-75 / SA-2 Guideline was manufactured by the Soviets from the
mid-1950s through to the 1980s, with spare part manufacture to support
exported installations continuing since then. The Chinese reverse
engineered the missile system during the 1960s, as the HQ-1, and then
produced indigenous improved HQ-2 variants thereafter. The Soviets and
Chinese have exported the weapon globally, and it would appear that
this system has been built in more variants and exported more widely
than any other SAM system.

Attempting to survey current global deployments of this system is a
challenging task. While Russia retired the system, it remains deployed
in large numbers by China, by many former Soviet Republics, some former
Warsaw Pact nations, and many former Soviet client nations in the
developing world. Much of Iran's air defence system comprises Chinese
supplied HQ-2s.

S-75 Battery Deployment

Russian
rendering of an SA-2 site with Fan Song E radar vans in
protected excavations (Almaz image).

An S-75 / SA-2 SAM site photographed by a
US reconnaissance aircraft during the Cuban Missile Crisis (US Air
Force).

An operational S-75 / SA-2 SAM site
photographed from low altitude by a US reconnaissance aircraft early
during the Vietnam conflict. Note the large number of radar and
generator vans, reduced in later variants of the system (US Air Force).

S-75 /
SA-2 Guideline Combat Imagery

US Air Force F-105D Thunderchief evading
an SA-2 missile over North Vietnam (US Air Force image).

SA-2
missile
in flight over the NVAF airfield at Kep (US Air Force image).

Above, proximity fused SA-2 round explodes
beneath a US Air Force RF-4C Phantom flown by Capts. Edwin Atterberry
and Thomas Parrott near Hanoi, 12th August, 1967. Below, the RF-4C
breaks up as a result of fatal structural damage. Both crew survived
the ejection, but Capt Atterberry was later killed in captivity by the
PAVN (US Air
Force image).

A damaged F-105D after a
near
miss by a proximity fused SA-2 round (US Air Force image).

The lethality of the SA-2 was so high that
it forced the development of specialised aircraft and systems to hunt
it. Above, the F-105F Wild Weasel, below the F-105G (US Air Force images).